Thinking out loud about port design

[DJ_Mittens 10+ year member]

I'm just thinking about port designs and their effects on sound.

Now, we have round and slotted ports. By my judgement, a round port would sound "best". Why? Because there is less turbulent surface for the moving air to warp around and cause port noise (forgive my lack of vocabulary). So a big vertical slot with the same surface area, but far more side (or turbulent) surface area would cause more port noise.

So what are the advantages of a slot port aside from the increased ease of building them?

Additionally, with understanding fluid dynamics, one great long tube would cause less turbulent noise and therefore get the cleanest sound from a ported enclosure. Why are so many made with such short ports, aside from the fact that they're easier to build into a small enclosure?

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[Goldtaz1 10+ year member]

I'm just thinking about port designs and their effects on sound.
Now, we have round and slotted ports. By my judgement, a round port would sound "best". Why? Because there is less turbulent surface for the moving air to warp around and cause port noise (forgive my lack of vocabulary). So a big vertical slot with the same surface area, but far more side (or turbulent) surface area would cause more port noise.

So what are the advantages of a slot port aside from the increased ease of building them?

Additionally, with understanding fluid dynamics, one great long tube would cause less turbulent noise and therefore get the cleanest sound from a ported enclosure. Why are so many made with such short ports, aside from the fact that they're easier to build into a small enclosure?

Unless you did something incredibly wrong in building a slot ported enclosure, the difference to your ears would be inaudible. There is no way (if you knew what you're doing) that you could hear the port noise with the subs in the trunk, hatch, or cargo area and your body in the driver's chair. However, I would venture to say that there would probably be an increase in SPL (maybe not much) by using a round/aero port because of the decrease in turbulence.

 

[DJ_Mittens 10+ year member]

So, basically you're foregoing ease of construction for a negligible increase in SPL.

I gotta get good at box design and actually test all these theories out.

 

[Beat_Dominator 5,000+ posts]

I agree, in car audio... there will be little difference. A slot port does have more friction than a round port though.

Why are so many made with such short ports, aside from the fact that they're easier to build into a small enclosure?

The port length is entirely decided by tune freq. and cross-sectional area. Usually, the smaller the port, the shorter it can be.

 

[tRiGgEr 5,000+ posts]

It is also much easier to build a port of 75 square inches in a slot port rather than a circle port. I also think they look better.

 

[Goldtaz1 10+ year member]

So, basically you're foregoing ease of construction for a negligible increase in SPL.
I gotta get good at box design and actually test all these theories out.

One of the single biggest reasons for using slot ports vs. round ports that I can think of is the fact that you can create more port area easier with slot ports than you can with round ports. The largest round/aero port being produced right now is a 6" diameter port which is only 28.2743338823081 square inches, where as you can do a port that is 10 X 10 and have 100 square inches. In this case it would take nearly (4) 6" diameter ports to equal (1) 10 X 10 cut out. That translates to more cut time with your jig saw //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif . I'm sure other folks might have a different view point, but I think many people will agree.

P.S. Not to mention there is the cost of buying a round/aero port vs. the cost of a little wood.

 

[SPL140.2 5,000+ posts]

I agree, in car audio... there will be little difference. A slot port does have more friction than a round port though.

Latex paint works well, wax, resin... //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[DJ_Mittens 10+ year member]

I'm not concerned about construction cost or difficulty, but rather getting the "most" out of a given sound system. If little things like a round, flared port can make a discernable difference versus a regular slot port, then why not take it? The flaring on the sides would cut down on turbulence a lot, but then the same could be done for a slotted port, though not quite as easily.

Thanks for the help guys.

 

[60ndown 10+ year member]

http://forum.elitecaraudio.com/showthread.php?threadid=107877

read on.........................

 

[DJ_Mittens 10+ year member]

Well that thread is way out of my league. I follow the gist of it, but having only bothered to take high school physics, I couldn't derive those formulas on my own. However, I don't see what that has to do with port design.